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Relocation and focal mechanism solutions of the MS6.9 Menyuan earthquake sequence on January 8,2022 in Qinghai Province
Xu Yingcai, Guo Xiangyun, Feng Lili
 doi: 10.11939/jass.20220008
[Abstract](186) [FullText HTML](16) [PDF 0KB](71)
Abstract:
On January 8, 2022, an MS6.9 earthquake occurred in Menyuan County, Haibei Prefecture of Qinghai Province. The earthquake ruptured a nearly 22 km long zone and strong tremors were felt through the regions of Qinghai, Gansu and Ningxia Province. In this paper, the early events of the Menyuan MS 6.9 earthquake sequence from January 8 to 12, 2022 were relocated by multi-step locating method. Meanwhile, the focal mechanism and focal depth of mainshock and MS≥3.4 after shocks were inverted by gCAP method. Based on focal mechanism result of the mainshock, the relative shear stress and normal stress on the two nodal planes of the focal mechanism solutions were also calculated under the existing stress field system. The result indicates that the initial rupture depth of Menyuan MS6.9 earthquake was 7.8 km, and the focal moment center depth was 4 km. The dominant initial rupture depths of early earthquake sequence were mainly between 7 and 8 km, while the focal moment center depth of MS≥3.4 after shocks varied between 3 km and 7 km. The focal depth profile shows that the sequence length within 24 hours after the mainshock was about 25 km, which was roughly consistent with the length of the surface rupture zone, and the overall sequence length was about 30 km. The early earthquake sequence, includes the MS6.9 mainshock and MS5.1 aftershock on January 8, located in the western part of the aftershock region, also includes the MS5.2 earthquake on January 12 located in the eastern part of the aftershock region. The focal mechanism solution of the MS6.9 main shock was strike 290°, dip 81°, rake 16° for the nodal plane I, and strike 197°, dip 74°, rake 171° for the nodal plane II. Based on the spatial distribution of aftershocks, it is estimated that the strike of the fault plane is 290 º, indicating that the earthquake is a left-lateral strike slip event on a nearly vertical fault plane. The results of focal mechanism solution of MS≥3.4 aftershocks show that these earthquakes were mainly strike-slip earthquakes, and the principal compressive stress axis varied from NE to EW from the west to the east of the aftershock region.Under the current stress field system, the relative shear stress generated on the nodal plane I of the Menyuan MS6.9 earthquake is 0.638, while on the focal mechanism solution nodal plane II is 0.522. The two focal mechanism nodal planes are not the maximum released nodal plane of the tectonic stress field, which is obviously different from the thrust focal mechanism of the Menyuan MS 6.4 earthquake in 2016, which is the optimal released nodal plane of tectonic stress field. Combined with the geological structure, focal mechanisms and aftershock distribution, the seismogenic structure of Menyuan MS6.9 earthquake on January 8, 2022 may be the western segment of Lenglongling fault, and its seismic dislocation mode is left-lateral strike-slip. According to the results of relocation, the magnitude-rupture relationship and the shear stress, it is concluded that there is a certain stress accumulation and stress has not been fully released in Menyuan area, and the risk of strong earthquakes still exists in this area.
Application of an optimized transmitting boundary with multiple artificial wave velocities in spectral-element simulation of seismic wave propagation
Xing Haojie, Liu Aiwen, Li Xiaojun, Chen Su, Fu Lei
 doi: 10.11939/jass.20210090
[Abstract](17) [FullText HTML](5) [PDF 2091KB](6)
Abstract:
This paper applied an optimized transmitting boundary with multiple artificial velocities (denoted as caj-MTF) that is recently proposed by the authors to the high-accuracy spectral-element simulation of seismic wave propagation, and made a comparison study with several other classical artificial (or absorbing) boundary conditions, which include Liao’s multi-transmitting formula (MTF) boundary, Perfectly Matched Layer (PML) boundary, viscous-spring boundary and first-order Clayton-Engquist paraxial-approximation boundary. The results obtained from theoretical analysis and numerical tests are as follows: ① The formulation of caj-MTF is very similar to that of MTF, so it has most of the advantages of the latter, i.e., very simple expressions, easy to be implemented, adjustable accuracy, minimal computation cost, and general applicability. ② Unlike the traditional MTF boundary that has only a single artificial wave velocity (i.e., computational wave velocity), caj-MTF has a set of artificial wave velocities corresponding to the boundary order. In the simulation of elastic waves, the computational wave velocity parameters of caj-MTF can be set to be P- and S-wave velocities, respectively. The consistency between computational and physical wave velocities makes a significant improvement in the boundary accuracy. ③ caj-MTF boundary has an slightly lower accuracy than that of PML boundary, whereas it is significantly superior to MTF, viscous-spring boundary and the first-order paraxial-approximation boundary. ④ caj-MTF is superior to PML as it has much simpler formulations and better versatility. This work provides a convenient and high-efficient artificial boundary (or absorbing boundary) for spectral-element simulation of seismic wave propagation.
Postseismic deformation observation,mechanism and lithospheric rheology of the central and northern Tibetan Plateau after the 2001 MW7.8 Kunlun earthquake:Insights and challenges
Zhao Dezheng, Qu Chunyan, Shan Xinjian, Zhang Guohong, Li Yanchuan, Gong Wenyu, Song Xiaogang
 doi: 10.11939/jass.20210058
[Abstract](32) [FullText HTML](5) [PDF 4927KB](14)
Abstract:
The 2001 MW7.8 Kokoxili earthquake was the largest earthquake in the central and northern part of the Tibetan Plateau in the recent half century. The large coseismic stress disturbance caused by the coseismic rupture drives and controls the significant postseismic deformation following this major earthquake. A decade of geodetic measurements documented large-spatial-scale, long-time-span and time-dependent postseismic deformation and their different evolution processes, and the geodetic measurements also revealed the complex fault kinematics characteristics, friction properties along fault strike and lateral heterogeneity of lithospheric rheological properties/structure in north-central Tibetan Plateau. In this paper, we briefly summarize postseismic deformation observations and their spatiotemporal characteristics of the Kokoxili earthquake based on InSAR time-series and GPS observations on a decadal scale. Particularly, the spatiotemporally dense InSAR observations are deemed as an important supplement to the postseismic GPS observations in this tectonic area. We summarize the models of large-scale postseismic deformation and the revealed postseismic deformation processes, various dynamic mechanisms and their relationships. Finally, we summarize the scientific understanding and unsolved scientific problems associated with the 2001 Kokoxili earthquake in the past 20 years: On the one hand, it is necessary to continuously observe and study the large-scale surface deformation of the Kunlun fault; On the other hand, the postseismic deformation model should be updated continuously to deepen our understanding of the earthquake cycle deformation of the Kunlun fault, the control of regional tectonics on earthquake cycle deformation, and the spatiotemporal evolution mechanism of complex fault movement in this region.
Spectral element method simulation of near-fault ground motions in complex sites based on CPU-GPU heterogeneous parallelism
Ba Zhenning, Zhao Jingxuan, Wu Mengtao, Liang Jianwen
 doi: 10.11939/jass.20210076
[Abstract](20) [FullText HTML](5) [PDF 3438KB](6)
Abstract:
Base on CUDA programming platform, the workstation-level CPU-GPU heterogeneous parallel method was implemented, and the spectral element method is used to simulate ground motion near-fault in real site. In this paper, the computational accuracy and efficiency of the proposed workstation-level CPU-GPU heterogeneous parallel method are tested by simulating the spontaneous rupture model TPV15 provided by SECE/USGS. Furthermore, the proposed method is applied to the simulation of M8.0 strong ground motion in 1679 Sanhe-Pinggu, and the applicability of the proposed method to the simulation of real ground motion is verified. The simulation results show that CPU-GPU heterogeneous parallel computing time is significantly reducedhan CPU parallel computing time, and the highest acceleration ratio is 3.04 and 2.16 times of CPU (36 core) and (72 core) respectively. The simulation results of M8.0 in Sanhe-Pinggu in 1679 clearly show the characteristics of near-fault ground motion, such as near-fault ground motion concentration, fault rupture directivity effect, velocity pulse and permanent displacement, and the influence of real terrain on near-fault ground motion. The results show that the CPU-GPU heterogeneous parallel method can effectively improve the computational efficiency of spectral element method simulation, and it has a good prospect to be applied to seismic wave field simulation of large-scale complex sites.
Numerical simulation of coupling failure between subway station and cross bridge
Dong Rui, Jing Liping, Shan Zhendong, Li Yadong
 doi: 10.11939/jass.20210078
[Abstract](71) [FullText HTML](15) [PDF 1726KB](3)
Abstract:
In this paper, a typical two-story and three-span subway station is taken as the research object. The nonlinear dynamic time-history analysis method is adopted to conduct numerical simulation analysis on the model of the subway station and the upper bridge in soft site. A potential coupling failure mode of subway station and bridge is presented. The seismic interaction between the subway station and the upper bridge is studied. Numerical simulation results show that: 1) the bridge has little effect on the seismic response of the station, and the damage of the station mainly depends on the earthquake action and structure strength. 2) The destruction of the subway station will cause a large horizontal and vertical deformation of the soil in adjacent area, and make the bridge beam fall; 3) After the destruction of the station, the bridge foundation makes the soil move towards the station, which aggravates the earthquake damage of subway station.
Analytical study on the topographic effect of Feitsui canyon
Gao Yufeng, Dai Denghui, Zhang Ning
 doi: 10.11939/jass.20210099
[Abstract](25) [FullText HTML](16) [PDF 0KB](5)
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The local amplification or attenuation of ground motion is often caused by the surface topography, which is due to the scattering phenomenon when the seismic wave propagates to the local topography. Although the topographic effect was first discovered in the anomalous seismic records, the ground motion data recorded by the topographic influence array are very few. There are five earthquakes recorded by six strong-motion accelerometers deployed along the Feitsui canyon recorded from the Hualien earthquake in 1992. Using our analytical theory of seismic wave propagation around a non-symmetrical V-shaped canyon, the strong motion accelerations of the site were simulated. The effects of topographic effect on the ground motion of the Feitsui canyon are revealed. The comparison between the simulated results and those ground motion accelerations recorded indicates that the proposed analytical theory of seismic wave propagation around V-shaped canyon is suitable for simulating the topographical effects on ground motions.
Variation law of optimal seismic peak intensity measures for underground structures with burial depth
Zhao Mi, Guo Mengyuan, Zhong Zilan, Du Xiuli
 doi: 10.11939/jass.20210094
[Abstract](21) [FullText HTML](13) [PDF 0KB](4)
Abstract:
Determination of a reasonable seismic intensity measure is very important for structural seismic performance evaluation. The seismic response of the underground structure is closely related to the deformation of the engineering site under earthquake excitation due to the constraint of the surrounding rock and soil. Besides, the burial depth of the underground structure also has critical effects on its seismic response. Therefore it is of great significance to investigate the variation of the optimal seismic intensity measure with burial depths of underground structures in engineering sites. In this paper, one-dimensional equivalent-linear earthquake site response analyses was performed by using 50 actual seismic records as the input motions to estimate the seismic response of homogeneous half-space sites and layered half-space sites. For the convenience of comparison among different numerical results, the engineering bedrock is assumed to be a linear elastic medium herein and the earthquake ground motions are input in the engineering bedrock at a same burial depth of 200 m from the ground surface. Based on the proficiency of the results, the optimal peak seismic intensity measure (peak ground acceleration PGA, peak ground velocity PGV, peak ground displacement PGD) varying with the burial depth of the site were investigated herein. The numerical results show that for the selected two types of sites, the optimal peak seismic intensity measure changes with the burial depth of the site. When the burial depth is small, the proficiency of PGA is the best. With the increase of the burial depth, the optimal proficiency changes from PGA to PGV. Moreover, although the critical burial depth corresponding to the transition from PGA to PGV are different for different sites, it exhibits linear correlation with shear wave velocity of the engineering sites.
Relocation of earthquakes in Tangshan area in the recent decade
Guo Lei, Sun Lina, Zhou Yi, Wang Ning
 doi: 10.11939/jass.20210029
[Abstract](242) [FullText HTML](48) [PDF 0KB](61)
Abstract:
We relocated 4 874 earthquakes totally which were recorded by Hebei seismic network in Tangshan area during the period between January of 2010 and July of 2020 by using the double-difference location method, the double-difference relocation method combined with waveform cross-correlation, and the double-difference tomography method combined with the waveform cross-correlation, respectively. The comparison of the location results by the three relocation methods suggests that the double-difference tomography method combined with the waveform cross-correlation could produce much higher resolution hypocentral parameters than those from the other two methods. As a result, the root-mean-square (RMS) of traveltime residuals were greatly reduced from 0.71 s to 0.27 s. In map view the relocated earthquakes are more concentrated on obvious strips around the faults, and the dominant distribution direction is NE, which is basically consistent with the fault strike in this area. The result is more reasonable in depth distribution with focal depth mainly concentrated in 5−15 km, and the distribution pattern appears as a nearly normal distribution. From the spatial distribution of the epicenters after relocation, it can be seen that there is a small earthquake dense zone with steep dip angle in NNE direction on the east of the Tangshan-Guye fault, indicating that the stress level is high and the tectonic activity is strong in this local area. Therefore it is speculated that there may be a hidden fault at the eastern end of the Tangshan-Guye fault, and the occurrence of earthquake in this region is related to its deep activities.
Afterslip distribution of 2017 Iran MW7.3 earthquake and its triggering effects on the 2018 MW6.0 earthquake
Jiang Ziqin, Yang Yinhui, Chen Qiang, Xu Qian, Xu Lang, Huang Xiaomei
 doi: 10.11939/jass.20200140
[Abstract](95) [FullText HTML](45) [PDF 3122KB](31)
Abstract:
In this study, a set of radar images acquired by the Sentinel-1 satellite that covers the interested seismically-effected area was collected. The time series surface deformation of the 283-day time span after the 2017 Sarpol Zahab, Iran, MW7.3 earthquake was extracted by using small baseline subset technique, then the two-step procedure inversion is carried out to obtain the afterslip model. In order to analyze the triggering effects of the 2017 strong earthquake and its post-seismic faulting on the 2018 Javanrud MW6.0 earthquake, the coseismic deformation field covering the whole MW6.0 earthquake region was obtained by using differential interferometry technique, and the inversion results of seismogenic fault parameters were used as receiving fault parameters for stress calculation. The results show that the post-seismic deformation of the Sarpol Zahab earthquake is mainly dominated by the afterslip effect. 283 days after the earthquake, the maximum accumulative slip of the after-slip model reaches up to 0.7 m. The co-seismic source model of the Javanrud MW6.0 earthquake indicates that the fault strike is 355.6°, the dip angle is 89.4°, and the movement is characterized by the right-lateral strike-slip together with some normal dip-slip component. Moreover, the calculated Coulomb stress modulation suggests that the MW7.3 earthquake and its afterslip have positive effect on triggering the subsequent Javanrud MW6.0 earthquake, and the occurrence of Javanrud earthquake could also be contributed by the regional plate activity.
S wave envelope synthesis based on different scattering patterns
Jing Yueling, He Lihao, Li Minghui, Zhang Yuxuan, Zheng Siyuan
 doi: 10.11939/jass.20200208
[Abstract](61) [FullText HTML](33) [PDF 2242KB](13)
Abstract:
In order to reveal the scattering process of seismic waves in the small scale inhomogeneous medium of the crust and to describe the envelopment broadening phenomenon of seismic waves more accurately. In this paper, based on the multiple anisotropic scattering theory, a discrete wave-number method is used to solve the improved seismic wave energy density integral equation, and the scattering pattern represented by Gaussian autocorrelation function is selected to obtain the S wave energy density envelope. Firstly, we analyzed the contribution of single scattering and multiple scattering to the energy density envelope of S wave. Then, we discussed the effects of absorption coefficient and total scattering coefficient on the synthesis of S wave energy density envelope. Finally, we compared the differences of the energy density envelope of S wave synthesized in different scattering patterns. The results show that: ① The contribution of single scattering and multiple scattering to the seismic wave scattering process is consistent, and for near earthquakes (less than 100 km), the single scattering model can be used to match the S-wave energy density envelope. As the hypocentral distance increases, the multiple forward scattering pattern can approach the total energy density envelope more quickly. ② As the absorption coefficient increases, the amplitude of the direct S wave and the coda wave will decrease. And while the total scattering coefficient increases, the amplitude of the direct S wave will decrease, but the coda wave amplitude of the S wave will increase. ③ In the forward scattering pattern, with the increase of hypocentral distance, the energy density envelope of S-wave appears the peak delay, the envelope is widened, and the attenuation consistency of the coda wave is accelerated.
Study on 2D in-plane HVSR simulation and application with transverse inhomogeneous body scattering
Ba Zhenning, Zhang Enwei, Liang Jianwen, Rong Mianshui
 doi: 10.11939/jass.20200177
[Abstract](39) [FullText HTML](53) [PDF 2405KB](15)
Abstract:
In order to analysis the significant influence of lateral inhomogeneity of site on HVSR curves. In order to analyze the influence, the diffuse field approach proposed by Sánchez-Sesma et al were adopted to simulate the HVSR curves of 2D alluvial canyons by calculating the imaginary part of Green’s functions of total wave field. Indirect boundary element method (IBEM) is used to solve the problem. The imaginary part of Green’s functions were solved by the stiffness matrix and Green’s functions respectively. The HVSR curves of 2D alluvial canyons and corresponding 1D layered half-space were analyzed. The influence of alluvial canyon’s shape and the relative position of calculation points on the HVSR curve was discussed emphatically. The results show that the influence of material impedance ratio on the HVSR curve is the most significant. With the increase of the material impedance ratio and the slope of the interface on the deposition side, the peak frequency of the first peak value of the HVSR curve increases significantly; the frequency of the first peak value of the HVSR curve on the alluvial canyon can be up to 3.3 times of the corresponding layered half-space result; the shape of the HVSR curve presents a plateau phenomenon. With the decrease of distance from the calculation point to the deposition boundary, the amplitude of HVSR curve in high frequency is relatively increase. According to the influence of local topography on HVSR curve, the HVSR method can be used to preliminarily determine the distribution location of local topography during site exploration to reduce exploration cost.
Study on earthquake focal mechanism and seismogenic structure of the Santai MS4.7 earthquake in 2013
Liu Suihai, Lü Jinxiong, Zhao Xueqin, Zhang Gang, Wen Mingru
 doi: 10.11939/jass20200201
[Abstract](112) [FullText HTML](52) [PDF 2203KB](34)
Abstract:
Santai MS4.7 earthquake occurred in Mianyang city, Sichuan Province on February 19, 2013. The epicenter located in an intersection area which combined the basement fracture in central Sichuan basin, the Mianyang-Santai-Dazu fracture and the Pujiang-Santai-Bazhong fracture. Based on the earthquake catalogue, seismic phase report and waveform data, we relocated the earthquake sequence, and solved the focal mechanism of the main earthquake by joint inversion of local and teleseismic waveforms, and also studied the seismogenic structure of the Santai MS4.7 earthquake according to the field geological survey. The spatial distribution direction of the relocated aftershock sequence is NW-SE and it highly fitted with the nodal plane I of the focal mechanism, the seismogenic structure of the earthquake can be considered as strike NW-SE, dip NE, and rupture plane is nearly vertical, and the seismogenic fracture was dextral strike-slip dislocation by the proximately horizontal confining pressure in the direction of nearly NS. During the field survey, any fracture marks nor surface ruptures can be obviously found, hence the seismic structure is concluded as a buried fault. The focal depths are 21.6 km and 19 km respectively through the relocation and joint inversion of local and teleseismic woweforms. The focal depth reflects that the location of the source area is in the low-velocity layer which is in the bottom of the upper-crust. This earthquake is caused during the adjusted and changed process of the tectonic stress field caused by Wenchuan earthquake, and it is the result of the reactivation of the high-angle fault concealed in the Presinian crystalline substrate in middle-block of Sichuan basin.
P-wave velocity changes in the source area before and after 2014 Yingjiang, Yunnan double earthquakes
Cao Ying, Qian Jiawei, Huang Jiangpei
 doi: 10.11939/jass.20200214
[Abstract](67) [FullText HTML](12) [PDF 7138KB](17)
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The time-lapse tomography method based on double-difference tomography can obtain high-precision seismic wave velocity changes. In this study, we applied this method to the seismic data set that is recorded by the Yunnan seismic network, so that we obtained the tempotal changes of P-wave velocity in the source area during the 2014 MS5.6 and MS6.1 Yingjiang earthquakes. The results showed that the spatial and temporal characteristics of the P-wave velocity of the crust at depth around the source area suggest co-seismic velocity reductions. After the MS5.6 earthquake occurred on May 24, the P-wave velocity of the crust dropped slightly. After the MS6.1 earthquake occurred on May 30, the P-wave velocity dropped definitely with an amplitude of about 1%. It showed that the amplitude of the reduction is related to the magnitude. We also reported that the temporal changes of P-wave velocity is also related to the aftershocks. It is possible that changes of dynamic and static stresses of the aftershocks caused changes of the physical properties in the source area. Finally, about five years after the Yingjiang earthquakes, a healing process is observed. And the rising level did not reach the previous falling level. However, this does not mean that the source area is still in the healing process.
Characteristics of Arias intensity and Newmark displacement of strong ground motion in Lushan earthquake
Li Xuejing, Xu Weijin, Gao Mengtan
 doi: 10.11939/jass.20200180
[Abstract](113) [FullText HTML](52) [PDF 3332KB](21)
Abstract:
The characteristics of spatial distribution, attenuation and correlation of ground motion parameters are important research contents in engineering seismology. In this paper, based on the ground motion records of Lushan earthquake, we study the spatial distribution and attenuation characteristics of Arias intensity and Newmark displacement as well as their correlation with other ground motion parameters, respectively. The results show that the spatial distribution of Arias intensity is related with the spatial distribution of seismic faults and the direction of earthquake rupture. Arias intensity has a good correlation with PGA. Furthermore, the site conditions have a significant effect on the correlation between the two: for the same PGA, the softer the site condition, the greater the Arias intensity. In addition, magnitude is also an important factor affecting the correlation between Arias intensity and PGA: with the same PGA, the greater the magnitude, the greater the Arias intensity. Newmark displacement has a good correlation with both PGA and Arias intensity, among which the correlation with Arias intensity is stronger, and the correlation coefficient can reach above 0.94. The research in this paper also shows that the existing models cannot describe the attenuation characteristics of Arias intensity and Newmark displacement of Lushan earthquake well, which indicates the particularity of Lushan earthquake in both the duration and rupture process. The particularity of Lushan earthquake reveals that the seismic geological and tectonic environment in Western China is significantly different from that in other regions. Therefore, the prediction equations of ground motion parameters suitable for earthquakes in Western China should be studied. The research results of this paper have important scientific significance and application value for us on both understanding the characteristics of ground motion and the prediction and prevention of earthquake disaster in China.
The conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves
Wang Xuliang, Jin Ping, Zhu Haofeng, Xu Henglei, Xu Xiong
 doi: 10.11939/jass.20200197
[Abstract](47) [FullText HTML](23) [PDF 2354KB](12)
Abstract:
The compensated liner vector dipole (CLVD)source is usually induced by underground explosions and could lead to a null in the Rg spectra. There is a theoretical scale between the null frequency and the depth of the CLVD source. Therefore we can estimate the depth of underground explosions with the null frequency. However, this relationship is based on simply considering the CLVD source while the conjunct effects of ISO and CLVD source are neglected. This study researches the conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves by numerical calculating the Rg spectra with seismology theory of surface waves. The results indicate that the null in mixed signals is quite different from the results of single CLVD source. Thus the null frequency of Rg waves is not simply corresponding to the theoretical value in practical underground explosions and it is improper to estimate the depth of explosions by directly applying the theoretical formula.
Problems and suggestions on site classification
Chi Mingjie, Li Xiaojun, Chen Xueliang, Ma Shengjie
 doi: 10.11939/jass.20200152
[Abstract](86) [FullText HTML](26) [PDF 1686KB](30)
Abstract:
The physical meaning of site classification is not clear in the current seismic design code for buildings, at the same time, the boundary of site classification is easy to cause the divergence of design ground motion parameters. For the above problems and deficiencies, some suggestions are given. To solve the problem that the physical meaning of site classification is not clear, on the basis of the current site classification method, according to the site classification index such as the covering layer thickness and the equivalent shear wave velocity, the sites are classified by two-level: the first level classification is consistent with the current one, which classifies sites based on the fundamental period of the site and the thickness of the overburden layer; the second level classification further considers the degree of hardness of the geotechnical medium based on the first level classification, and sub-classification according to equivalent shear wave velocity. Based on the current research on seismic disaster and seismic motion characteristics of thick soft site, combined with the development of long-period constructions, the site classification is expanded from the original four categories to five categories, at the same time, the boundary of each classification, especially the boundary of class II, III and IV sites, is limited from the original open type, which can effectively avoid the problem of divergence of design ground motion parameters caused by site classification. The related research results can provide reference for site classification and determination of design ground motion parameters.
The dynamic mechanical response of the fault under different water injection schedules
Zhu Aiyu, Sun Zihan, Jiang Changshen, Chen Shi, Zhang Dongning, Cui Guanglei
 doi: 10.11939/jass.20210137
[Abstract](663) [FullText HTML](35) [PDF 2416KB](48)
Abstract:
Water injection used in industry can lead to the activation of existing faults and have induced many destructive earthquakes. Therefore, it is of great significance to study the dynamic response of faults under water injection to explore the mechanism of induced earthquakes. The poroelastic spring-slider model calculates the fault stability under three kinds of classical water injection schedules (ascending, rapidly ascending, descending and intermittent) using poroelastic coupling numerical simulation. The results show that, with the continuous injection of fluid, the pore pressure inside the fault will go through three stages: slow rise, rapid rise, and stable rise. For different water injection schedules, the three stages are not fully reflected, and the forms are different; under the same water injection schedule, the smaller the reservoir permeability is, the greater the pore pressure near the wellhead is, the smaller the pore pressure at fault is, and the greater the difference of pore pressure between the two is; the larger the value is, the easier the earthquake will be induced. The value is negatively correlated with the fluid pressure of injected reservoir fluid but positively correlated with the change rate of fluid pressure; the critical stiffness increases rapidly in the early stage due to the increase of the change rate of pore pressure and decreases in the later stage due to the influence of pore pressure. The rapid rising and falling water injection schedule greatly increase the possibility of inducing earthquake in the early stage of water injection. The intermittent water injection schedule causes a large change of necessary stiffness in the late stage of water injection, which increases the possibility of inducing an earthquake. This study can provide the quantitative scientific basis for the risk assessment of water injection-induced earthquakes and reduce the possibility of water injection-induced earthquakes.
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Characteristics of seismic ambient noise in Sichuan region
Xie Jiangtao, Lin Liping, Zhao Min, Chen Liang
2021, 43(5): 533-550.   doi: 10.11939/jass.20200148
[Abstract](228) [FullText HTML](112) [PDF 4209KB](66)
Abstract:
Based on the three-component continuous waveform data recorded by sixty permanent seismic stations in Sichuan seismic network from January 1, 2015 to December 31, 2018, this paper calculated the noise power spectral densities and corresponding probability density functions, then gave the statistical characteristics of noise power spectral density at different frequencies, and finally analyzed the characteristics of noise level at different regions and frequencies. The results show that the high-frequency seismic noises of most stations are affected by the nearby human activities, production mode and lifestyle, which has obvious seasonal and diurnal variations. The noise level increases during summer and decreases during winter with the lowest level during the Spring Festival in the whole year; and the geographical distribution is not obvious. For double-frequency microseisms, the noise level increases during winter and decreases during summer, and has obvious seasonal variation with an average of 1−5 dB, which has obvious geographical distribution characteristics. The average noise level in eastern Sichuan is the highest, followed by Panxi region, and the lowest in western Sichuan Plateau. The microseism peaks have different amplitudes and occur at different frequencies in summer and winter, with the peaks shifted by 1−2 s toward longer periods in the winter. Compared with the double-frequency microseism band, the noise energy at primary microseism band is weaker, the seasonal variation is not obvious, and the difference of noise level in geographical distribution is significantly reduced. While the long-period (>20 s) noise level has no obvious seasonal variation and no difference in geographical distribution. In addition, installing seismographs in caves and borehole can effectively reduce the influence of noise sources, temperature and pressure on high-frequency band and long-period observations, therefore the noise level is lower than that of shallow installations.
Spatio-temporal characteristics of repeating seismic events in the middle of Tianshan orogenic belt
Tang Lanlan, Zhang Yifeng, Yao Daoping
2021, 43(5): 551-568.   doi: 10.11939/jass.20200192
[Abstract](216) [FullText HTML](83) [PDF 9835KB](68)
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Based on the seismic waveform data recorded in the stations of Xinjiang regional seismic network from 2009 to 2017, the repeating earthquakes in the middle of Tianshan orogenic belt and its periphery in Xinjiang were determined and relocated by using the waveform cross correlation technique and the master event approach. The results show that 11 618 of the 30 181 events are repeating events, which consist of 2395 groups of doublets and clusters, accounting for 38.5% of the total events. According to the statistical results of the distance between doublets before and after repeating events relocation, it is estimated that the system location error in the research area is about 5−10 km. In addition, combined with the latest source classification results in this area, the results show that repeating earthquakes of different source types have different spatial and temporal distribution characteristics. Repeating quarry blasts appear mostly as clusters, 93.6% of them occur during the daytime, and they also exhibit a seasonal pattern with more events in summers and fewer ones in winters. Tectonic earthquakes occurred in various thrust faults in the Tianshan orogenic belt, and occurred randomly at any time, and the monthly frequency of tectonic events is relatively stable during the studied period. Repeating induced earthquake locations indicate that most of them are located near large gas/oil fields and water reservoirs, but some also geographically overlay tectonic earthquakes in some regions. The occurring time characteristics of induced earthquakes are similar to those of tectonic earthquakes, which appears as random distribution within 24 hours.
Structural characteristics of Yanyuan basin deduced from seismic survey and its dynamic implication
Zhang Pingchuan, Yu Changqing, Qu Chen, Qiu Longjun, Li Hengqiang
2021, 43(5): 569-583.   doi: 10.11939/jass.20200119
[Abstract](444) [FullText HTML](220) [PDF 4061KB](83)
Abstract:
In this paper, an artificial seismic line and a short period natural seismic array covering Yanyuan basin are set up. The seismic energy attribute is extracted from the artificial seismic data, and the seismic velocity structure is obtained by seismic tomography. Meanwhile the S-wave velocity distribution at different depths is obtained by inverting the empirical Green’s functions retrieved from cross-correlation of the ambient noise data recorded by the short period seismic array. The results show that Yanyuan basin is mainly divided into three layers by seismic characteristics. The shallow layer is the Cenozoic sedimentary stratum with low P wave velocity ranging from 1.0 km/s to 2.1 km/s, and it is characterized by good continuity and strong reflection. The S wave velocity is low in the south and high in the middle of Yanyuan basin, and the trend of the low-velocity anomaly in the south is in agreement with the strike of Yanyuan fault. Cenozoic basin is thick in the south and thin in the north, where the sedimentary and structure are controlled by Yanyuan fault. The middle layer is medium-low P wave velocity ranging from 3.5 km/s to 4.5 km/s, and it is characterized by discontinuous reflection axis and weak reflection, which can be interpreted as Triassic strata. The S-velocity becomes higher gradually and the change becomes smaller in general. The deep layer is high velocity, characterized by chaotic seismic reflection and weak reflection energy, interpreted as Paleozoic strata. Furthermone, there is a detachment surface in the upper crust, which is the interface between sedimentary and basement. A series of faults are developed from the detachment to the surface, and these faults are also an earthquake-prone area in Yanyuan basin. One of the faults is Jinhe-Qinghe fault, which is the boundary fault between Yanyuan basin and Kangdian block.
Anomalous characteristics of geomagnetic vertical strength polarization before the 2017 Milin MS6.9 earthquake in Tibet
Li Xia, Feng Lili, Zhao Yuhong, Liu Lei, Gou Zhidong, Fan Wenjie, He Manqiu, Liao Xiaofeng, Aisa Yisimayili
2021, 43(5): 584-594.   doi: 10.11939/jass.20200196
[Abstract](312) [FullText HTML](167) [PDF 5394KB](44)
Abstract:
Based on the second sampling data from 65 geomagnetic stations in Chinese mainland, we extracted the ultra-low frequency electromagnetic anomaly signals from the epicenter of the 2017 Milin MS6.9 earthquake in Tibet and its vicinity using geomagnetic vertical strength polarization method, and analyzed their spatio-temporal evolution characteristics. The results show that a large range of geomagnetic vertical strength polarization high value anomalies appeared in the Qinghai-Xizang (Tibetan) Plateau before the MS6.9 earthquake, and the abnormal process lasted for nine days. The high value anomaly began on October 30, 2017. The high value lasted for three days, followed by a short period of decline, a turning point and an increase. Afterwards the high value anomaly appeared again and lasted for four days. In this process, the time-series curves of each high-value station show single peak or double peak. The spatial distribution map shows that high value anomalies occur repeatedly in the western part of Chinese mainland, especially at the junction of Bayankhara and Qiangtang blocks on the Tibetan Plateau. The anomaly appeared, expanded, contracted, disappeared, expanded and disappeared, and the abnormal area reached its maximum value on October 31. Ten days after the end of the abnormal process, the Milin MS6.9 earthquake occurred, with its epicenter 5 km from the anomaly threshold line of October 31. Comprehensive analysis indicates that this anomaly has strong temporal and spatial correlation with the Millin earthquake and can be regarded as reliable seismic electromagnetic precursor.
Interference characteristics of new energy power generation on electromagnetic observation environment:Taking the electromagnetic observation of Xuzhuangzi station of Tianjin as an example
Ma Yong, Li Ning, Xu Xuegong, Bi Jinmeng
2021, 43(5): 595-604.   doi: 10.11939/jass.20210028
[Abstract](79) [FullText HTML](72) [PDF 1871KB](25)
Abstract:
New energy power generation is an important measure taken by the countries to replace non-renewable energy sources so as to achieve sustainable utilization of power resources under the sustainable development strategy. Wind power and photovoltaic power generation are clearly defined as the key development fields of renewable energy. These big power generation facilities will have a great impact on the original seismic observation environment. Based on the electromagnetic observation project of the Xuzhuangzi station of Tianjin, aiming at the wind power and photovoltaic power generation facilities in the observation area around the station in recent years we analyzed the temporal and spatial changes of electromagnetic observation data in different observation environments by the field experimental measurement, and summarized the influence characteristics of the construction and operation of wind power generation and photovoltaic power generation on electromagnetic observation environment interference. The results show that the impact of wind turbine is significantly less than that of photovoltaic power system on the electromagnetic observation environment, which can be regarded as an interference point to regulate the distance between wind turbine and observation facilities. In order to ensure that the photovoltaic power system does not affect the electromagnetic observation, it is necessary to treat each system as a whole and maintain a sufficiently large separation distance between them. This paper can provide a reference for the protection and evaluation of electromagnetic observation environment by building similar new energy power generation equipment in the seismic field, which is of important practical significance for protecting the observation environment of seismic stations.
Design and implementation of ionospheric multi-parameter anomaly monitoring system in Sichuan-Yunnan region
Liu Jiang, Xu Rui, Chen Cong, Rao Taiguo, Li Xingquan
2021, 43(5): 605-614.   doi: 10.11939/jass.20210038
[Abstract](54) [FullText HTML](50) [PDF 3018KB](11)
Abstract:
This paper introduced the design ideas and function implementation of ionospheric multi-parameter anomaly monitoring system in Sichuan-Yunnan region, and then applied the system to monitoring test of the MS6.0 earthquake on June 17, 2019 in Changning, Sichuan. The results show that the system realizes the real-time monitoring of abnormal changes such as global and China regional VTEC, site VTEC and foF2, which is helpful to carry out the demonstrative seismic-ionospheric anomaly monitoring. The graphic and data results can provide evidences for the identification of seismic-ionospheric anomalous disturbance, and ionospheric precursor information for earthquake monitoring and prediction in Sichuan-Yunnan region.
Dynamic characteristics of fault hydrogen concentration in Aksu and its earthquake reflecting efficiency
Zhong Jun, Wang Bo, Yan Wei, Ma Yuchuan
2021, 43(5): 615-627.   doi: 10.11939/jass.20210007
[Abstract](88) [FullText HTML](29) [PDF 2762KB](34)
Abstract:
This paper firstly analyzed the periodic components of the fault hydrogen concentration observation data in Aksu, and then explored the relationship between temperature, atmospheric pressure and the annual periodic components of hydrogen concentration using the linear regression and cross-correlation methods, respectively. At the same time, the Molchan error diagram method was used to quantitatively verify the earthquake reflecting efficiency of fault hydrogen in Aksu. The results show that: ① Fault hydrogen concentration in Aksu has clear annual and semi-daily periodic components; ② There is a significant positive correlation between the annual dynamic changes of fault hydrogen concentration and temperature, and a general correlation between the annual dynamic changes of hydrogen concentration and atmospheric pressure, indicating that the annual periodic changes of hydrogen concentration are mainly affected by temperature. The results from Molchan error diagram method show that the fault hydrogen concentration anomaly in Aksu is more sensitive to moderate-strong earthquakes around the observation point, suggesting better earthquake reflecting efficiency.
Empirical prediction models of time-averaged shear wave velocity vS20 and vS30 in Sichuan and Yunnan areas
Jia Lin, Xie Junju, Li Xiaojun, Wen Zengping, Chen Wenbin, Zhou Jian
2021, 43(5): 628-642.   doi: 10.11939/jass.20200193
[Abstract](130) [FullText HTML](67) [PDF 3535KB](49)
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The time-averaged shear wave velocity of overburden soil is an important parameter for site classification and reflecting site effects on ground motion, which is widely used in earthquake ground motion prediction models. Using the lithology and wave velocity profile data of 973 boreholes in Sichuan and Yunnan, we study the regional prediction model of the average shear wave velocity. Based on the bottom constant velocity (BCV) model, log-linear model and Markov independent model, the empirical prediction models of vS20 and vS30 in this region were established. The results show that, the BCV method has the largest prediction error. When the depth of the shear wave velocity is less than 10 m, this method will significantly underestimate the average wave velocity of the actual site. Based on the log-linear model of Boore method, we establish an empirical prediction model. By comparison, we find that the average wave speed prediction results in Sichuan and Yunnan are close to those in Beijing and California, and significantly lower than those in Japan. Through the comparative analysis of prediction error of three different extrapolation methods, we find that the prediction results based on Markov independence model have the smallest error at different depths, and it is preferred to use this method to set up regional prediction model.
Construction and verification of onsite ground motion prediction models for seismic intensity instrument
Peng Chaoyong, Zheng Yu, Xu Zhiqiang, Jiang Xudong, Yang Jiansi
2021, 43(5): 643-655.   doi: 10.11939/jass.20210075
[Abstract](309) [FullText HTML](159) [PDF 2127KB](118)
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Using the initial P-wave early warning parameters to construct onsite ground motion prediction models, so as to quickly release an alarm message when it reaches the predefined threshold, is a key issue of the onsite earthquake early warning system, which is directly related to the accuracy and timeliness of the early warning information. For micro-electro-mechanical-systems-based seismic intensity instrument with poor data quality, the obtained displacement record after two integrations has a large deviation, which will lead to more false and missed alarms. Therefore, for waveforms recorded by seismic intensity instrument, in this paper, we adopted Butterworth filters of different orders (1−4) to build up several onsite ground motion prediction models based on the P-wave 3 seconds data and the whole P-wave window. These models are the relationships between displacement amplitude PD and peak ground velocity PGV, PD and peak ground acceleration PGA, velocity amplitude PV and PGV, PV and PGA, acceleration amplitude PA and PGV, PA and PGA, respectively. The models are then verified using the collected micro-electro-mechanical-systems-based seismic event records from the Sichuan-Yunnan Demonstration Early Warning Network. The results show that for the seismic intensity instrument records, the two optimal onsite ground motion prediction models are the relationship between PV and PGV and the one between PA and PGA obtained by the first-order Butterworth filter processing and derived from the whole P-wave window. In specific applications, two or more statistical relationships should be simultaneously adopted to predict onsite ground motion, and observed ground motion values should be used as additional judgment conditions to reduce the probability of false and missed alarms.
The development in seismic application research of VLF/LF radio waves
Zhang Xuemin
2021, 43(5): 656-673.   doi: 10.11939/jass.20210143
[Abstract](121) [FullText HTML](60) [PDF 2147KB](45)
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Radio waves from very low frequency and low frequency (VLF/LF) transmitters, as an active signal for communication and navigation purpose, show great advantages in ionospheric monitoring and application research with their long-distance propagation feature in the waveguide between surface and lower ionosphere. This paper summarized the developments in detecting technology of VLF/LF radio waves, their data analysis methods, case study and statistical research, coupling processes and channels in lithosphere-atmosphere-ionosphere. On the basis of the significant achievements of this technology in earthquake application, and the researches in the origin of big disturbances in VLF/LF observations, the future development plan has been considered to build up a stereo-monitoring system in China by combining our long-history ground-based network and new satellite platform in electromagnetic field, to fully use of this technology in earthquake research.
The anomaly characteristics of water temperature in the Eryuan well before the 2021 Yangbi MS6.4 earthquake in Yunnan,China
Ma Yuchuan, Yan Rui, Hu Xiaojing
2021, 43(5): 674-677.   doi: 10.11939/jass.20210142
[Abstract](183) [FullText HTML](61) [PDF 2528KB](86)
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